(1) Field of the Invention
The present invention relates to the field of jacks.
Particularly the present invention relates to the field of vibration jacks which are controlled and driven by servo-valves. These jacks have a characteristic frequency which is essentially a function of the volume of the chamber or chambers, of the force developed, and of the moving mass.
(2) Description of the Prior Art
As stated above, the characteristic frequency of a jack is dependent upon thechamber volume, force developed and the moving mass. As an illustration of this dependency for a given jack, the larger the moving mass, the lower the hydraulic characteristic frequency. This hydraulic characteristic frequency dependency on chamber volume, force development and mass has disadvantages. One disadvantage is that a loss of operational control over the jack occurs with an overpressurization of the chamber or chambers. The overpressurization of the chamber is difficult to overcome, particularly at low frequencies. This difficulty is related to the hydraulic characteristic frequency dependency upon chamber volume, developed force and mass. As this frequency is lowered it develops greater energy or force. This increase in force or energy hampers the elimination of overpressurization because greater pressure is required to overcome the force.
The prior art discloses various attempts to eliminate this overpressurization. These attempts have mainly involved the increasing of the working section of the chambers. This is accomplished by putting the volumes of the chamber, which are separated by the piston, into communication with each other. While this reduces overpressurization it necessarily involves sacrificing part of the efficiency.
Accordingly, the present invention has as one of its objects the ability to reduce the overpressurization without reducing the efficiency.
Another object of the present invention is the reduction of overpressurization by absorbing the increase of energy at lower frequencies.